This invention pertains to a web processing machine, and more particularly, to a slitter scorer of the general type described in U.S. Pat. Nos. 4,214,495; 4,215,609 and 4,242,934. In addition to slitting and scoring a moving web into two or more narrow webs, the apparatus of said patents also can process mill run board. Mill run board is corrugated paper board which has not been slit or scored but is trimmed only along its edges to a preselected width. In an automatic slitter scorer wherein slitter knives are set electronically without direct operator intervention, a problem has been encountered when producing mill run board. The problem is that the mill run board which has been trimmed has a finished width which is greater than the preselected width at which the knives were set.
The present invention is directed to a solution of the problem of obtaining trimmed mill run board of a preselected width. I noted that the mill run board does not remain flat while being trimmed. While traveling along the upper web path the mill run board sags in the center. On the other hand, when mill run board travels along the lower web path, the center of the web bows upward.
This phenonemon is believed to be caused by the disposition of the trim chutes. Because of space limitations the vacuum trim chute for the upper web path is placed above a web support table located adjacent the downstream end of the slitter scorer and the vacuum trim chute for the lower web path is placed below a web support table. The suction from the upper trim chutes exerts an upward force on the ends of the web while the suction from the lower trim chutes exerts a downward force on the ends of the web. The centers of the webs react in a direction opposite to these forces.